Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!decwrl!sgi!shinobu!odin!thestepchild!rhartman
From: rhartman@thestepchild.sgi.com (Robert Hartman)
Newsgroups: comp.unix.shell
Subject: Re: Creating a lock file in csh?
Message-ID: <1991Apr17.183652.12420@odin.corp.sgi.com>
Date: 17 Apr 91 18:36:52 GMT
References: <1991Apr15.205654.26253@unhd.unh.edu> <1991Apr16.175347.1082@odin.corp.sgi.com> <1991Apr17.102654.4476@athena.mit.edu>
Sender: news@odin.corp.sgi.com (Net News)
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 20

In article <1991Apr17.102654.4476@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
>
>Let's assume that two processes are trying to get a lock in this way at
>the same time over NFS.  There is no way in the NFS protocol to open a file
>for write if it does not exist in an atomic operation.  Therefore, NFS client
>kernels first have to check with the server to see if the file exists, and
>send a request to create it if it doesn't.  So here's what could happen:
>
>  [ description of resulting race condition omitted ]
>
>-- 
>Jonathan Kamens			              USnail:

Thank you Jonathan!

I guess the real solution would be for someone to write a "lock" command
that makes the NFS lock manager accessible at the user level.  Don't think
I'll hold my breath though ... ;^)

-r